**2.1. Application of mineral fertilizers**

Annually, sugarcane production fields are amended with inorganic sources of N, P, and K as well as other, more sporadic, amendments, such as Ca, Mg, sulfur (S), and micronutrients. However, the macronutrients, such as P, K, Ca, Mg, and S, are also fundamental for the development of sugarcane and when used in association, they could reflect increases of productivities.

rates, changes in *Ascomycota* and *Basidiomycota* abundance were detected in these soils, with *Basidiomycota* abundance negatively affected by increasing N dose [17]. Gumiere et al. [18] evaluated the diversity and abundance of fungal communities in soils used for the cultivation of sugarcane and demonstrated that the distribution of fungal species abundance fits better a neutral model that assumes biogeographical patterns than models that assume envi-

Multi-Analytical Interactions in Support of Sugarcane Agroecosystems Sustainability in Tropical…

from soils, and pH was the parameter that explained the majority of this share [37]. Nitrous oxide production was confirmed *in vitro* as a common trait of fungi [38]. Considering the

understand the processes that result in the release of gas in sugarcane soils, since the crop grows predominantly in acidic soils (**Table 1**). In addition, since N application changes the

O emissions attributed to fungi, this subject needs to be covered to

**N source Annual** 

**N-N2 O emission (g ha−1)**

531

350

2165

410

)<sup>2</sup> 329

O released

7

O produced by this group of soil

http://dx.doi.org/10.5772/intechopen.71180

**Soil OM (%)**

**Sampling events** **Time covered (days)**

**Soil pH**

– 286 5.1 2.3 41 278

– 1700 4.8 2.8<sup>d</sup> 38 328

– 12,200 4.9 16.9<sup>d</sup> 38 343

ronmental filtering. Recently, fungi have being presented as contributors to the N<sup>2</sup>

**Soil type Redox status**

drained

drained

DCD

DCD-R

DMPP

DMPP-R

Removed Oxisol Well-

120 Urea +

120 Urea +

120 Urea +

120 Urea +

120 Ca(NO<sup>3</sup>

9.4 t ha−1 Lixisol Well-

120 Urea 2301

120 PSCU 353

 Urea 2600 Urea 3600 PCU 3952a DMPP 2300<sup>b</sup> Removed Urea 1976<sup>c</sup>

> Gleysol Floodplain

 Urea 23,200 Urea 28,200 PCU 16,100 DMPP 20,700 removed Urea 16,000

fungal community, it may also change the balance of N<sup>2</sup>

**Straw blanket**

relevance of pH to the N<sup>2</sup>

**(kg ha−1)**

0 3rd

0 5th

0 1st

ratoon

ratoon

Burnt (2.9 t ha−1 remained)

**Crop stage**

ratoon

microorganisms.

**Reference N dose** 

Soares et al. [19]

Wang et al. [32]

Urea is considered the most widely used N fertilizer in sugarcane fields, followed by ammonium sulfate and ammonium nitrate [29]. However, more than 25% of the N applied in the form of urea to surface soil during the sugarcane ratoon cycles can be volatilized to ammonia [29]. Consequently, urea is applied only during the sugarcane vegetative stage in Brazil. The use of liquid urea with crop residue blankets has been reported to avert N volatilization in Australia [30]. Both urease and nitrifier inhibitors can alternatively be used to reduce N losses as ammonia [31].

Nitrification, i.e., the biological oxidation of ammonia into nitrite, followed by the oxidation of nitrite into nitrate can produce nitrous oxide (N<sup>2</sup> O) as a by-product. Soares et al. [19] reported reduced N<sup>2</sup> O emissions from a sugarcane field in Brazil after DMPP (3,4-dimethylpyrazole phosphate)-coated urea applications (**Table 1**), with fewer effects on the microbial community diversity and composition in comparison with treatments using urea or calcium nitrate. However, Wang et al. [32] did not find similar results for well-drained soil in Australia (**Table 1**), even after applying three times more DMPP-coated urea than that used on the Brazilian soil. These results may be at least in part due to the expected differences in soil microbial communities between the soil types and geographical regions.

Archaea and bacteria are key drivers of N in the redox process of denitrification of nitrate to form N<sup>2</sup> O in the soil [20]. Soares et al. [19] showed that N<sup>2</sup> O emissions in sugarcane soils were significantly correlated with bacterial *amo*A genes but not with denitrification-related genes (*nir*K, *nir*S, and *nos*Z), suggesting that ammonia-oxidizing bacteria via nitrification are the main contributors to emissions of N<sup>2</sup> O when urea is used as a fertilizer. In turn, Fracetto et al. [33] showed an increase in denitrifying gene abundance (*nir*S, *nir*K, *nor*B, and *nos*Z) after ammonium nitrate application to the soil, with N<sup>2</sup> O emissions associated with *nor*B gene abundance. However, denitrification may contribute to much of the N<sup>2</sup> O emissions from sugarcane cultivation systems [19, 34], and denitrification is at least in part associated with soil moisture content [35]. In soils with 75% water-filled pore space (WFPS), denitrification has been shown to be the most important process in N<sup>2</sup> O emissions, while nitrification has been shown to be the most important process in soils with 60% WFPS [35]. Denitrification is a respiratory process that regularly occurs in the absence of O<sup>2</sup> , in which NO<sup>3</sup> − is used as an electron acceptor. However, although large denitrification rates are associated with low concentrations of O<sup>2</sup> , aerobic denitrification has also been demonstrated for some bacteria [34].

The N fertilizer dose has been associated with changes in microbial communities [13, 17] and in abundance of functional genes associated with nitrification and denitrification in the sugarcane soil and rhizosphere [36]. Although fungal species richness in the sugarcane soil and rhizosphere has not shown variation to N fertilizer applied to the soil at different rates, changes in *Ascomycota* and *Basidiomycota* abundance were detected in these soils, with *Basidiomycota* abundance negatively affected by increasing N dose [17]. Gumiere et al. [18] evaluated the diversity and abundance of fungal communities in soils used for the cultivation of sugarcane and demonstrated that the distribution of fungal species abundance fits better a neutral model that assumes biogeographical patterns than models that assume environmental filtering. Recently, fungi have being presented as contributors to the N<sup>2</sup> O released from soils, and pH was the parameter that explained the majority of this share [37]. Nitrous oxide production was confirmed *in vitro* as a common trait of fungi [38]. Considering the relevance of pH to the N<sup>2</sup> O emissions attributed to fungi, this subject needs to be covered to understand the processes that result in the release of gas in sugarcane soils, since the crop grows predominantly in acidic soils (**Table 1**). In addition, since N application changes the fungal community, it may also change the balance of N<sup>2</sup> O produced by this group of soil microorganisms.

**2.1. Application of mineral fertilizers**

6 Sugarcane - Technology and Research

tion of nitrite into nitrate can produce nitrous oxide (N<sup>2</sup>

the main contributors to emissions of N<sup>2</sup>

after ammonium nitrate application to the soil, with N<sup>2</sup>

been shown to be the most important process in N<sup>2</sup>

ratory process that regularly occurs in the absence of O<sup>2</sup>

microbial communities between the soil types and geographical regions.

O in the soil [20]. Soares et al. [19] showed that N<sup>2</sup>

abundance. However, denitrification may contribute to much of the N<sup>2</sup>

productivities.

as ammonia [31].

reported reduced N<sup>2</sup>

to form N<sup>2</sup>

tions of O<sup>2</sup>

Annually, sugarcane production fields are amended with inorganic sources of N, P, and K as well as other, more sporadic, amendments, such as Ca, Mg, sulfur (S), and micronutrients. However, the macronutrients, such as P, K, Ca, Mg, and S, are also fundamental for the development of sugarcane and when used in association, they could reflect increases of

Urea is considered the most widely used N fertilizer in sugarcane fields, followed by ammonium sulfate and ammonium nitrate [29]. However, more than 25% of the N applied in the form of urea to surface soil during the sugarcane ratoon cycles can be volatilized to ammonia [29]. Consequently, urea is applied only during the sugarcane vegetative stage in Brazil. The use of liquid urea with crop residue blankets has been reported to avert N volatilization in Australia [30]. Both urease and nitrifier inhibitors can alternatively be used to reduce N losses

Nitrification, i.e., the biological oxidation of ammonia into nitrite, followed by the oxida-

pyrazole phosphate)-coated urea applications (**Table 1**), with fewer effects on the microbial community diversity and composition in comparison with treatments using urea or calcium nitrate. However, Wang et al. [32] did not find similar results for well-drained soil in Australia (**Table 1**), even after applying three times more DMPP-coated urea than that used on the Brazilian soil. These results may be at least in part due to the expected differences in soil

Archaea and bacteria are key drivers of N in the redox process of denitrification of nitrate

were significantly correlated with bacterial *amo*A genes but not with denitrification-related genes (*nir*K, *nir*S, and *nos*Z), suggesting that ammonia-oxidizing bacteria via nitrification are

et al. [33] showed an increase in denitrifying gene abundance (*nir*S, *nir*K, *nor*B, and *nos*Z)

arcane cultivation systems [19, 34], and denitrification is at least in part associated with soil moisture content [35]. In soils with 75% water-filled pore space (WFPS), denitrification has

shown to be the most important process in soils with 60% WFPS [35]. Denitrification is a respi-

acceptor. However, although large denitrification rates are associated with low concentra-

, aerobic denitrification has also been demonstrated for some bacteria [34]. The N fertilizer dose has been associated with changes in microbial communities [13, 17] and in abundance of functional genes associated with nitrification and denitrification in the sugarcane soil and rhizosphere [36]. Although fungal species richness in the sugarcane soil and rhizosphere has not shown variation to N fertilizer applied to the soil at different

O emissions from a sugarcane field in Brazil after DMPP (3,4-dimethyl-

O) as a by-product. Soares et al. [19]

O emissions in sugarcane soils

O emissions from sug-

is used as an electron

O emissions associated with *nor*B gene

O emissions, while nitrification has been

−

O when urea is used as a fertilizer. In turn, Fracetto

, in which NO<sup>3</sup>



Sugarcane fields are widely distributed around the globe in tropical regions, and the crop grows both in deep well-drained soils and in floodplains (**Figure 1** and **Table 1**). This contrast limits the conclusion about which processes predominate in sugarcane fields. While the

DCD, dicyandiamide; DMPP, dimethylpyrazole phosphate; PSCU, polymer sulfur coated urea; PCU, polymer coated

O fluxes reach their highest values in the field and that this result would be due to the sum

Concerning the GHG emissions in sugarcane soils amended with mineral fertilizers, the emissions based on ammonium nitrate sources can vary from 1811 g ha−1 to 5237 g ha−1 [20, 26], and from 0.85 to 1.68% when urea is applied to the Brazilian tropical soils [19, 23, 32]. In

broadly depending on the soil redox status and N dose applied (**Table 1**). The emission factor

O produced by both nitrification and denitrification processes. However, this hypothesis still needs to be addressed in a variety of soils to improve the understanding of the processes

O y−1 in the floodplains, the amount drops to

O y−1, on average, in well-drained soils. When analyzing the

O) emissions from sugarcane production fields after nitrogen fertilizers applications to

O fluxes, Denmead et al. [40] verified that at 70% of WFPS, the

O released and, consequently, the fertilizer emission factor vary

emissions can reach more than 20 kg ha−1 N-N<sup>2</sup>

O release in sugarcane soils.

approximately 2.4 kg ha−1 N-N<sup>2</sup>

effect of water saturation on N<sup>2</sup>

Australia, the amount of N<sup>2</sup>

N2

of N<sup>2</sup>

that result in N<sup>2</sup>

**Reference N dose** 

Allen et al. [30]

Paredes et al. [39]

a

b

c

**(kg ha−1)**

0 3rd and 4th ratoon

0 2nd

urea; Vin., vinasse; FC, filter cake.

<sup>d</sup>Obtained based on TOC\*1.724.

**Table 1.** Annual nitrous oxide (N<sup>2</sup>

tropical soils with contrasting characteristics.

Estimated from the plot.

ratoon

**Crop stage**

**Straw blanket**

Kept Hydrosol

**Soil type Redox status**

2 × 50 Liquid urea 3860 100 Liquid urea 3930 2 × 100 Liquid urea 5810 200 Liquid urea 9560

Kept Oxisol Well-

100 (NH<sup>4</sup>

118 (NH<sup>4</sup>

18 Vin. 18 Vin.

Floodplain

drained

presented <sup>118</sup> (NH<sup>4</sup>

Calculated based on data available at Results section (52% higher than treatment with 80 kg urea).

Calculated based on data available at Results section (24% lower than treatment with 80 kg urea).

)2

)2 SO<sup>4</sup> +

)2 SO<sup>4</sup> +

Vin.

Vin.

SO<sup>4</sup> Not

**N source Annual** 

Multi-Analytical Interactions in Support of Sugarcane Agroecosystems Sustainability in Tropical…

**N-N2 O emission (g ha−1)**

**Soil pH**

– 2860 ~5 5.2<sup>d</sup> 30 ~365

– 3920 5.4 2.6<sup>d</sup> 69 211

**Soil OM (%)**

http://dx.doi.org/10.5772/intechopen.71180

**Sampling events** **Time covered (days)**

9

Multi-Analytical Interactions in Support of Sugarcane Agroecosystems Sustainability in Tropical… http://dx.doi.org/10.5772/intechopen.71180 9


DCD, dicyandiamide; DMPP, dimethylpyrazole phosphate; PSCU, polymer sulfur coated urea; PCU, polymer coated urea; Vin., vinasse; FC, filter cake.

a Calculated based on data available at Results section (52% higher than treatment with 80 kg urea).

b Estimated from the plot.

**Reference N dose** 

Carmo et al. [23]

Pitombo et al. [26]

Pitombo et al. [20] **(kg ha−1)**

8 Sugarcane - Technology and Research

0 1st

0 Plant cane

0 1st

100 2nd

ratoon

ratoon

**Crop stage**

ratoon

**Straw blanket** **Soil type Redox status**

drained

drained

drained

Removed Oxisol Well-

120 Removed NH<sup>4</sup>

120 7 t ha−1 NH<sup>4</sup>

120 14 t ha−1 NH<sup>4</sup>

120 21 t ha−1 NH<sup>4</sup>

142 Removed NH<sup>4</sup>

142 7 t ha−1 NH<sup>4</sup>

142 14 t ha−1 NH<sup>4</sup>

142 21 t ha−1 NH<sup>4</sup>

– Lixisol Well-

85 – Urea + Vin.

Removed Oxisol Well-

61 Vin. 2583 37 Concentrated

0 10 t ha−1 \_\_\_ 1810

61 Vin. 3490 37 Concentrated

0 t ha−1 Oxisol Well-

100 NH<sup>4</sup>

161 NH<sup>4</sup>

100 NH<sup>4</sup>

161 NH<sup>4</sup>

100 5.6 t ha−1 NH<sup>4</sup>

100 8.5 t ha−1 NH<sup>4</sup>

100 11.3 t ha−1 NH<sup>4</sup>

60 – Urea 1377 60 – Urea + Vin. 2212 85 – Urea + Vin. 3261

**N source Annual** 

NO<sup>3</sup> 2091

NO<sup>3</sup> 3286

NO<sup>3</sup> 3019

NO<sup>3</sup> 4170

3024

5869

7034

7464

3566

3763

2106

5699

2500

NO<sup>3</sup> 5237 5.2 2.8 37 246

NO<sup>3</sup> 1811

NO<sup>3</sup> 2870

NO<sup>3</sup> 4548

NO<sup>3</sup> 3204

NO<sup>3</sup> 3347

NO<sup>3</sup> + Vin.

NO<sup>3</sup> + Vin.

– 577 4.5 2.2 20 314

– 1605 5.1 2.3 48 274

NO<sup>3</sup> + Vin.

NO<sup>3</sup> + Vin.

NO<sup>3</sup> + Vin.

NO<sup>3</sup> + Vin.

+ FC

Vin.

Vin.

NH<sup>4</sup>

drained

**N-N2 O emission (g ha−1)**

**Soil pH**

– 107 4.5 2.2 21 335

**Soil OM (%)**

**Sampling events** **Time covered (days)**

> c Calculated based on data available at Results section (24% lower than treatment with 80 kg urea). <sup>d</sup>Obtained based on TOC\*1.724.

**Table 1.** Annual nitrous oxide (N<sup>2</sup> O) emissions from sugarcane production fields after nitrogen fertilizers applications to tropical soils with contrasting characteristics.

Sugarcane fields are widely distributed around the globe in tropical regions, and the crop grows both in deep well-drained soils and in floodplains (**Figure 1** and **Table 1**). This contrast limits the conclusion about which processes predominate in sugarcane fields. While the emissions can reach more than 20 kg ha−1 N-N<sup>2</sup> O y−1 in the floodplains, the amount drops to approximately 2.4 kg ha−1 N-N<sup>2</sup> O y−1, on average, in well-drained soils. When analyzing the effect of water saturation on N<sup>2</sup> O fluxes, Denmead et al. [40] verified that at 70% of WFPS, the N2 O fluxes reach their highest values in the field and that this result would be due to the sum of N<sup>2</sup> O produced by both nitrification and denitrification processes. However, this hypothesis still needs to be addressed in a variety of soils to improve the understanding of the processes that result in N<sup>2</sup> O release in sugarcane soils.

Concerning the GHG emissions in sugarcane soils amended with mineral fertilizers, the emissions based on ammonium nitrate sources can vary from 1811 g ha−1 to 5237 g ha−1 [20, 26], and from 0.85 to 1.68% when urea is applied to the Brazilian tropical soils [19, 23, 32]. In Australia, the amount of N<sup>2</sup> O released and, consequently, the fertilizer emission factor vary broadly depending on the soil redox status and N dose applied (**Table 1**). The emission factor for flooded areas has reached values higher than 20% [32, 40]; for well-drained areas, it has reached up to 1% for the standard fertilizer doses, but it increases for higher N doses [30].

sources of dissolved organic matter in soils, and its release into solution occurs through physicochemical decomposition and leaching from litter and formation of humic substances [55]. Omori et al. [52] reported increases in bacterial diversity after vinasse application to the soil and revealed that this by-product of the sugar-ethanol industry promotes the participation of soil microbial community members in N and Fe cycling. The authors showed that *Acidobacteria* Gp3 and Gp4 were most abundant in the vinasse-amended soil. In addition, bacterial community members belonging to *Actinomycetales* were more diverse in vinasseamended soil than in soils without vinasse. Navarrete et al. [14] reported effects of combined applications of vinasse and N fertilizer to the soil on bacterial communities in sugarcane soils. *Acidobacteria*, *Actinobacteria*, and *Verrucomicrobia* were the bacterial phyla most affected

Multi-Analytical Interactions in Support of Sugarcane Agroecosystems Sustainability in Tropical…

addition of both vinasse and N fertilizer to the soils, thus increasing the microbial-N biomass, decreasing the microbial-C biomass and altering the soil chemical factors that were correlated with the microbial biomass. Regarding the soil chemical factors, the K and S were negatively correlated with microbial biomass and the soil pH was positively correlated with microbial-C biomass. The long-term organic inputs has evidenced clear trend of increasing microbial-C biomass when compared with conventional practice management [47, 56]. In turn, Dias [53] reported that vinasse can increase the abundance of nitrous oxide reductase (*nos*Z) gene but not the copy number of both nitrite reductase (*nir*K) and methyl coenzyme-M reductase

While vinasse is broadcast on the soil during the vegetative stage and on the ratoons, filter cake is typically used only during the vegetative sugarcane stage with mineral fertilizer added in the furrows (**Table 1**). Using a molecular approach based on 16S rRNA gene sequencing, Omori [57] revealed *Actinobacteria* as the predominant phylum in the bacterial community related to the degradation of plant biomass and the production of antimicrobials in sugarcane soil containing filter cake semi-composting, which is possibly related to the high amount of lignocellulosic material available in the filter cake. The authors also reported *Firmicutes* and *Proteobacteria* in the soil at different stages of the composting process. In turn, Hernández et al. [58] used a culture-dependent approach and showed that filter cake application to the sugarcane soil increases colonies of phosphate-solubilizing microorganisms, total bacteria, and fungi. In addition, Tellechea et al. [59] showed higher microbial activity in sugarcane soil with

an important indicative that the microorganisms present in the filter cake are able to increase available P in the soil solution and then to improve its absorption by plants, which can be highlighted in the tropical soil condition, such as Oxisol, that has high P content adsorbed in

Carmo et al. [23] and Siqueira Neto et al. [25] provided a comprehensive characterization of GHG emissions associated with the use of vinasse and filter cake as organic fertilizer application practices for planting and regrowth of sugarcane were commonly used in Brazil. Carmo et al. [23] reported significant differences in daily fluxes from soils with organic fertilizers and those with no fertilizer (organic or mineral) (**Table 1**). Daily fluxes from soils that included the application of filter cake and vinasse in combination with mineral fertilizer were significantly

and N<sup>2</sup>

O emissions shortly after the

http://dx.doi.org/10.5772/intechopen.71180

11

determination. These results are

in these soils. The authors identified increases in CO<sup>2</sup>

filter cake application based on traditional methods of CO<sup>2</sup>

the soil by the internal sphere complex (unavailable for plants).

(*mcr*A) genes in sugarcane soils.

The carbon dioxide (CO<sup>2</sup> ) and methane (CH<sup>4</sup> ) emissions in sugarcane soils are also directly related to the N fertilizer dose [23] and its effects on the metabolizable nutrient availability [22] and the soil microbial community [13]. Urea may be metabolized by *Nitrospira*, resulting in ammonia and CO<sup>2</sup> [41]. For instance, urea applied in pure form or as part of other organic amendments is hydrolyzed and results in CO<sup>2</sup> . Urease is produced by a broad range of soil organisms—from bacteria to plants [42]. There are also possible indirect effects. The N fertilizers in agriculture also affect the soil capacity to consume CH<sup>4</sup> [43]. The oxidation of NH<sup>4</sup> + and CH<sup>4</sup> are homologous functions, and they can be mediated by the same enzyme in methane-oxidizing bacteria and ammonia-oxidizing bacteria [44, 45]. This implies that NH<sup>4</sup> + can inhibit the oxidation of CH<sup>4</sup> by competing for active sites [43, 45]. The specificity of a bacterial group in relation to another can cause the collapse of competition between groups either because of lack of energy or source of C, since the accumulation of toxic species of N follows the evolution of the oxidation of NH<sup>4</sup> + , which results in low consumption of CH<sup>4</sup> and greater availability of N for nitrification, denitrification, and formation of N<sup>2</sup> O.

#### **2.2. Use of organic fertilizers**

As an alternative to mineral fertilization in sugarcane production fields, waste products from ethanol production (vinasse and filter cake), sewage sludge, green manures, inoculants of atmospheric N-fixing bacteria and phytohormones are commonly applied to the soil in the form of organic fertilizer to promote plant growth [46]. These organic fertilizers represent an important contribution of the N, P, K, and organic matter, mainly soil labile organic fractions, such as dissolved organic C and N, and others C-light organic fractions [47–49], in the sugarcane agroindustry [25]. Soil labile organic C can be defined as the soil organic matter fraction that sustains the soil food web and therefore directly influences nutrient cycles and many biologically related soil properties [50].

The filter cake, a solid organic residue of the sugarcane processing in the mill that is rich in P, is used mainly in cane-plants, at 10–30 t ha−1 when applied in the furrow and, 80–100 t ha−1 when applied in the total area, in pre-planting, replacing the phosphate fertilization partially or totally, depending on the dose of P<sup>2</sup> O5 recommended. The vinasse is mainly used in sugarcane, supplying all the K<sup>2</sup> O and part of the N, being very poor in P. Vinasse, depending on its chemical composition and soil fertility, is applied in the range of 60–120 m<sup>3</sup> ha−1 by tank vehicles or 150–250 m<sup>3</sup> ha−1 by irrigation-sprinkler [51].

Although organic fertilizers are used to increase sugarcane productivity through nutrient availability to plants, they can also affect soil microbial community and physicochemical soil factors [7, 14, 20, 52], and key biogeochemical processes associated with GHG emissions, such as decomposition, respiration, nitrification and denitrification [23, 25, 53]. Moreover, the use of organic residues has resulted in the increase of C and N labile organic forms [47–49], which has been used as soil quality indicator due to rapid alteration according to soil practice management [54]. It is generally assumed that plant litter and humus are the two most important sources of dissolved organic matter in soils, and its release into solution occurs through physicochemical decomposition and leaching from litter and formation of humic substances [55].

for flooded areas has reached values higher than 20% [32, 40]; for well-drained areas, it has reached up to 1% for the standard fertilizer doses, but it increases for higher N doses [30].

related to the N fertilizer dose [23] and its effects on the metabolizable nutrient availability [22] and the soil microbial community [13]. Urea may be metabolized by *Nitrospira*, result-

of soil organisms—from bacteria to plants [42]. There are also possible indirect effects. The

methane-oxidizing bacteria and ammonia-oxidizing bacteria [44, 45]. This implies that NH<sup>4</sup>

terial group in relation to another can cause the collapse of competition between groups either because of lack of energy or source of C, since the accumulation of toxic species of N follows

As an alternative to mineral fertilization in sugarcane production fields, waste products from ethanol production (vinasse and filter cake), sewage sludge, green manures, inoculants of atmospheric N-fixing bacteria and phytohormones are commonly applied to the soil in the form of organic fertilizer to promote plant growth [46]. These organic fertilizers represent an important contribution of the N, P, K, and organic matter, mainly soil labile organic fractions, such as dissolved organic C and N, and others C-light organic fractions [47–49], in the sugarcane agroindustry [25]. Soil labile organic C can be defined as the soil organic matter fraction that sustains the soil food web and therefore directly influences nutrient cycles and many

The filter cake, a solid organic residue of the sugarcane processing in the mill that is rich in P, is used mainly in cane-plants, at 10–30 t ha−1 when applied in the furrow and, 80–100 t ha−1 when applied in the total area, in pre-planting, replacing the phosphate fertilization partially

its chemical composition and soil fertility, is applied in the range of 60–120 m<sup>3</sup> ha−1 by tank

Although organic fertilizers are used to increase sugarcane productivity through nutrient availability to plants, they can also affect soil microbial community and physicochemical soil factors [7, 14, 20, 52], and key biogeochemical processes associated with GHG emissions, such as decomposition, respiration, nitrification and denitrification [23, 25, 53]. Moreover, the use of organic residues has resulted in the increase of C and N labile organic forms [47–49], which has been used as soil quality indicator due to rapid alteration according to soil practice management [54]. It is generally assumed that plant litter and humus are the two most important

O5

) emissions in sugarcane soils are also directly

O.

recommended. The vinasse is mainly used in sug-

O and part of the N, being very poor in P. Vinasse, depending on

. Urease is produced by a broad range

[43]. The oxidation of

+

and greater

[41]. For instance, urea applied in pure form or as part of other

by competing for active sites [43, 45]. The specificity of a bac-

, which results in low consumption of CH<sup>4</sup>

are homologous functions, and they can be mediated by the same enzyme in

) and methane (CH<sup>4</sup>

N fertilizers in agriculture also affect the soil capacity to consume CH<sup>4</sup>

+

availability of N for nitrification, denitrification, and formation of N<sup>2</sup>

organic amendments is hydrolyzed and results in CO<sup>2</sup>

The carbon dioxide (CO<sup>2</sup>

10 Sugarcane - Technology and Research

ing in ammonia and CO<sup>2</sup>

can inhibit the oxidation of CH<sup>4</sup>

**2.2. Use of organic fertilizers**

the evolution of the oxidation of NH<sup>4</sup>

biologically related soil properties [50].

or totally, depending on the dose of P<sup>2</sup>

vehicles or 150–250 m<sup>3</sup> ha−1 by irrigation-sprinkler [51].

arcane, supplying all the K<sup>2</sup>

and CH<sup>4</sup>

NH<sup>4</sup> + Omori et al. [52] reported increases in bacterial diversity after vinasse application to the soil and revealed that this by-product of the sugar-ethanol industry promotes the participation of soil microbial community members in N and Fe cycling. The authors showed that *Acidobacteria* Gp3 and Gp4 were most abundant in the vinasse-amended soil. In addition, bacterial community members belonging to *Actinomycetales* were more diverse in vinasseamended soil than in soils without vinasse. Navarrete et al. [14] reported effects of combined applications of vinasse and N fertilizer to the soil on bacterial communities in sugarcane soils. *Acidobacteria*, *Actinobacteria*, and *Verrucomicrobia* were the bacterial phyla most affected in these soils. The authors identified increases in CO<sup>2</sup> and N<sup>2</sup> O emissions shortly after the addition of both vinasse and N fertilizer to the soils, thus increasing the microbial-N biomass, decreasing the microbial-C biomass and altering the soil chemical factors that were correlated with the microbial biomass. Regarding the soil chemical factors, the K and S were negatively correlated with microbial biomass and the soil pH was positively correlated with microbial-C biomass. The long-term organic inputs has evidenced clear trend of increasing microbial-C biomass when compared with conventional practice management [47, 56]. In turn, Dias [53] reported that vinasse can increase the abundance of nitrous oxide reductase (*nos*Z) gene but not the copy number of both nitrite reductase (*nir*K) and methyl coenzyme-M reductase (*mcr*A) genes in sugarcane soils.

While vinasse is broadcast on the soil during the vegetative stage and on the ratoons, filter cake is typically used only during the vegetative sugarcane stage with mineral fertilizer added in the furrows (**Table 1**). Using a molecular approach based on 16S rRNA gene sequencing, Omori [57] revealed *Actinobacteria* as the predominant phylum in the bacterial community related to the degradation of plant biomass and the production of antimicrobials in sugarcane soil containing filter cake semi-composting, which is possibly related to the high amount of lignocellulosic material available in the filter cake. The authors also reported *Firmicutes* and *Proteobacteria* in the soil at different stages of the composting process. In turn, Hernández et al. [58] used a culture-dependent approach and showed that filter cake application to the sugarcane soil increases colonies of phosphate-solubilizing microorganisms, total bacteria, and fungi. In addition, Tellechea et al. [59] showed higher microbial activity in sugarcane soil with filter cake application based on traditional methods of CO<sup>2</sup> determination. These results are an important indicative that the microorganisms present in the filter cake are able to increase available P in the soil solution and then to improve its absorption by plants, which can be highlighted in the tropical soil condition, such as Oxisol, that has high P content adsorbed in the soil by the internal sphere complex (unavailable for plants).

Carmo et al. [23] and Siqueira Neto et al. [25] provided a comprehensive characterization of GHG emissions associated with the use of vinasse and filter cake as organic fertilizer application practices for planting and regrowth of sugarcane were commonly used in Brazil. Carmo et al. [23] reported significant differences in daily fluxes from soils with organic fertilizers and those with no fertilizer (organic or mineral) (**Table 1**). Daily fluxes from soils that included the application of filter cake and vinasse in combination with mineral fertilizer were significantly increased in comparison with those observed in the treatment that included only mineral fertilizer. Cumulatively, the highest emissions were observed for ratoon sugarcane treated with vinasse, especially as the amount of crop residue on the soil surface increased. Normally, the flow of CH<sup>4</sup> is variable, indicating the ability of the soil to serve either as source or as sink of this GHG [53]. In general, filter cakes can be associated with a lower emission factor compared with other organic or synthetic fertilizers [25]. In turn, the vinasse application can increase N2 O emissions from sugarcane soils, especially during the first couple of days after application [26, 53]. The applied vinasse generates a high emission factor analogous to the emission factor observed for urea application.

N-fixing biofertilizers are useful to economize the nitrogenous fertilizers and to increase the cane yield. N inputs to the soil can naturally occur as a consequence of the metabolism of N<sup>2</sup>

Multi-Analytical Interactions in Support of Sugarcane Agroecosystems Sustainability in Tropical…

of energy generated is very expensive, requiring much ATP; for this region, nitrogenases are

[69]. However, in sugarcane, endophytic symbiosis with N<sup>2</sup>

is known to occur, and they have been reported for more than 25 years [70]. Although biological N fixation is a natural process in sugarcane, it can be optimized by using more specific and efficient bacteria. The multiplicity of beneficial effects of microbial inoculants, particularly plant growth promoters, emphasizes the need for further strengthening their research and

Soil residue management focusing in soil quality (conservation) and its energetic use are emerging study subjects regarding the sugarcane crop worldwide. In areas under sugarcane cultivation, different sugarcane harvest systems are commonly applied, such as manual handling with burnt sugarcane (burnt harvest) and mechanical harvesting (green harvest). In Brazil, the world's largest producer of sugarcane, harvest practices for sugarcane are undergoing a change, with the increased introduction of mechanical harvesting. This change is regulated by state legislation. For instance, the states of São Paulo and Goiás, which produce more than half of the sugarcane in Brazil, have similar deadlines to completely change their harvest systems. In these states, sugarcane burning is scheduled to be completely phased out progressively during the next 15 years, depending mainly on land declivity due to mechani-

Without burning, in average, 8–30 Mg ha−1 dry mass of straw is generated [9, 71, 72], which has 54% dry leaves and 46% tops [73]. The average crop residue produced every year is approximately 10 Mg ha−1 of material with a C:N ratio of approximately 100 [74], that reflects the presence of lignocellulosic composition in the straw, which accounts for 19–34% lignin, 29–44% cellulose, and 27–31% hemicelluloses [75–79]. This characteristic implies in high recalcitrance of residues, that has slow decomposition rate on soil. Around 30–60% of soil moisture content is kept after harvest [80, 81]. There is discussion regarding the feasibility of sugarcane biomass utilization in the industry versus keeping it in the field to improve soil quality and

Both practices in sugarcane harvest, i.e., burnt and green harvests, have the potential to influence soil physicochemical, microbiological factors, as well as, soil organic fractions. Sugarcane burning as a preharvesting method is a millenary technique to eliminate all leaves and tops around the sugarcane plant, which helps with manual harvest [82] and transport [83]. However, it is known that burnt harvest has the potential to negatively alter the physical, chemical, and biological soil characteristics [21, 84], to increase GHG emissions [85–87], and to decrease soil organic matter [88]. Moreover, particulate matter and smoke from leaf burning

reduction by nitrogenases is an exergonic process, the flow

fixing microbes. Even though N<sup>2</sup>

use in sugarcane agriculture.

**3. Crop residue and harvest management**

inhibited by NH<sup>3</sup>

zation limitations.

guarantee the long-term sustainability.

released into the atmosphere represent health hazards [89].


13


http://dx.doi.org/10.5772/intechopen.71180

Another organic fertilizer is sewage sludge. Although sewage sludge is also very lacking in K, it has high levels of P [60]. This organic fertilizer can improve soil's physical and chemical characteristics and can increase sugarcane productivity, acid phosphatase activity, and biomass [61]. These authors also highlighted the beneficial effect of B, Zn, and Cu from sewage sludge in association with available P that provided increase in the stalks production. However, its use requires some care, as there is the possibility of pathogen and heavy metal contamination. The application of sewage sludge may increase the concentrations of As, Cd, Cu, Ni, Pb, and Zn in the soil, and the quality standard established by the legislation for agricultural soils must be respected [62]. However, the incorporation into soils of sewage sludge rich in C has been shown to increase the amount of dissolved organic matter in soils. Dissolved organic matter can facilitate metal transport in soil through formation of soluble metal-organic complexes [63, 64]; in contrast, they are also able to mobilize some heavy metals sorbed from soil or sewage sludge, being the soil organic matter one of the most important solid phases that adsorb heavy metals, such as Cu and Cd in acid sandy soils. Thus, soils amended with sewage sludge display different physicochemical properties, especially in terms of dissolved organic matter in soil, which will affect behavior of metals in soils. The application of sewage sludge can also provide an increase in CO<sup>2</sup> emissions in soils [65]. However, the impact of sewage sludge in the environment on the soil microbial community has not yet been reported for sugarcane agriculture.

The incorporation of ecological practices into sugarcane production and management has the potential to arrest and ameliorate the negative effects of monocropping on soil degradation and yield decline. Historically, the production of green manure as a cover or break crop has been shown to improve the physical, chemical, and biological characteristics of the soil for many crops in production agriculture. Schumann et al. [66] published an interesting review of green manuring practices in sugarcane production. However, only recently, the effects of green manure on soil microbial populations, diversity, and activity in sugarcane soils have been reported [67], in which decrease in the total bacterial population in the soil was revealed, while that of fungi and actinomycetes increased. In addition, Ambrosano et al. [68] verified that green manure is an alternative source of N for sugarcane crops and can supplement or even replace mineral N fertilization. Moreover, green manure associated with mineral N fertilizer altered the soil chemical factors, increasing Ca and Mg contents, sum of bases, soil pH and base saturation, and as a consequence decreased the potential acidity.

N-fixing biofertilizers are useful to economize the nitrogenous fertilizers and to increase the cane yield. N inputs to the soil can naturally occur as a consequence of the metabolism of N<sup>2</sup> fixing microbes. Even though N<sup>2</sup> reduction by nitrogenases is an exergonic process, the flow of energy generated is very expensive, requiring much ATP; for this region, nitrogenases are inhibited by NH<sup>3</sup> [69]. However, in sugarcane, endophytic symbiosis with N<sup>2</sup> -fixing microbes is known to occur, and they have been reported for more than 25 years [70]. Although biological N fixation is a natural process in sugarcane, it can be optimized by using more specific and efficient bacteria. The multiplicity of beneficial effects of microbial inoculants, particularly plant growth promoters, emphasizes the need for further strengthening their research and use in sugarcane agriculture.
